/*
 * Reverse Linked List II 
 * Reverse a linked list from position m to n. Do it in-place and in one-pass
 * For example: Given 1->2->3->4->5->nullptr, m = 2 and n = 4,
 * return 1->4->3->2->5->nullptr
 */

#include "../../func.h"

ListNode *reverseBetween(ListNode *head, int m, int n)
{
    ListNode dummy(-1);
    dummy.next = head;

    ListNode *prev = &dummy;
    for (int i = 0; i < m-1; ++i)
        prev = prev->next;
    ListNode *head2 = prev;

    prev = head2->next;
    ListNode *cur = prev->next;
    for (int i = m; i < n; ++i)
    {
        prev->next = cur->next;
        cur->next = head2->next;
        head2->next = cur;
        cur = prev->next;
    }

    return dummy.next;
}